The abrupt departure of the popular Mordechai could shake up the field for Israel's May 17 national elections. Some analysts think it hurts Netanyahu's chances of staying in power.

The prime minister immediately announced that he would offer the defense portfolio to Moshe Arens, Netanyahu's former political mentor -- who, ironically, is challenging him for the Likud leadership in a primary to be held Monday.

Arens, 73, a former general who has served as defense minister, said he would consider the offer after Monday's vote.

The prime minister accused Mordechai of negotiating simultaneously with Likud and with a new centrist party, which reportedly is poised to nominate Mordechai for prime minister if he bolts Likud.

"In recent days and weeks, I have seen that your personal ambition is stronger than anything else," Netanyahu wrote in a letter to Mordechai, which he read at a news conference Saturday evening. "Our ways must part.... You can no longer serve as defense minister in a Likud government."

Netanyahu said Mordechai had demanded assurances that he would be named defense minister if Likud stayed in power, and turned to the centrist party when Netanyahu refused.

During Netanyahu's announcement, Mordechai was meeting at his home with the co-founders of the new centrist party to discuss the group's platform. Among those attending was former army chief Amnon Lipkin-Shahak, who has already announced his candidacy for prime minister.

Shaking with anger, Mordechai accused the prime minister of sending him "a letter full of lies, slander and inaccuracies that are appropriate for a petty politician."

"I'm sorry to say that the prime minister is no longer worthy of my personal support or, I suppose, the support of the Israeli people," he said. "Israel deserves a better leadership."

Mordechai, 54, a former general and a strong supporter of the peace process with the Palestinians, had kept Israel in suspense for weeks over whether he would turn against Netanyahu. Speculation had mounted after the defense minister failed to nominate himself as a Likud candidate for a seat in parliament before Friday's deadline.

If he were to become the centrist party candidate, Mordechai, who is of Kurdish ancestry, would appeal to voters with family origins in the Arab world -- until now a mainstay of Likud support. Surveys have shown he would beat Netanyahu in a race for prime minister.